Antenna calibration device

ABSTRACT

A coupling device includes a plurality of couplers. Each coupler includes a transmission main line and a coupling subline. The transmission main line is used for providing an input end and an output end. The coupling subline is coupled with the transmission main line to provide two coupling ends. The coupling subline includes two first parts located on opposite sides of the transmission main line and a second part connected between the two first parts. The coupling sublines of the plurality of couplers are connected in series to provide a first coupling output port and a second coupling output port. The first part of the coupling subline of at least one of the plurality of couplers has a shared section with the second part of the coupling subline of an adjacent one of the plurality of couplers.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority under 35 U.S.C. § 119 to ChinesePatent Application No. 201810548253.0, filed May 31, 2018, the entirecontent of which is incorporated herein by reference as if set forth inits entirety.

FIELD OF THE INVENTION

The present invention generally relates to antennas and, moreparticularly, to a multi-channel calibration device for an antennaarray.

DESCRIPTION OF RELATED ART

Adaptive antenna arrays that include a plurality of radiating elementsare widely used in modern mobile communication systems. These antennaarrays are often referred to as “smart” antennas. By adjusting theamplitude and phase characteristics of radio frequency (“RF”) signalstransmitted to the radiating elements, a smart antenna can generatespatially directional radiation patterns or “antenna beams” that can bedirected to cover a selected area or to point at individual users. Theuse of smart antennas may significantly improve the capacity and linkquality of a communication system.

Smart antennas include beamforming networks that adjust the amplitudeand/or phase of the RF signals that are passed to the radiatingelements. In a base station including a smart antenna, signalstransmitted by an RF transceiver enter the beamforming network throughan RF port. In the beamforming network, the signals are divided intosub-components that travel along multiple paths (which are also referredto as “channels”) that correspond to multiple radiating elements or tomultiple groups (e.g., columns) of radiating elements. The signals ineach path undergo independent adjustments of their amplitude and phasecharacteristics (which is referred to as “beamforming”). The beamformedsignals along the multiple paths are passed to the correspondingradiating elements or corresponding groups of radiating elements. Eachradiating element or each group of radiating elements generates anindependent, spatially directional beam. After interference andsuperimposition of the independent beams, the resulting compositeantenna beam may exhibit good directivity.

In order to form a desired antenna beam, it is desirable to make surethat transmission/reception paths from the RF transceiver to theradiating elements or columns of radiating elements are uniform in termsof their amplitude and phase characteristics, so that the compositeantenna beam may have the shape and characteristics of the antenna beamthat is expected to be obtained by adjustment of the beamformingnetwork. However, in practice it can be difficult to ensure that thecharacteristics of the multiple transmission/reception paths areuniform, and any differences between the paths may seriously degrade theperformance of the smart antenna. Thus, calibration devices may be usedto identify and compensate for differences between the multiple paths.

Calibration devices are known in the art that collect respectiveportions of the signals traversing each transmission/reception path andoutput the collected energy at a calibration port of the antenna. FIG. 1is a schematic diagram illustrating the basic structure and principle ofsuch a prior art calibration device 20. The calibration device 20 inFIG. 1 is implemented in an antenna having an antenna array thatincludes eight radiating units 10. Each radiating unit 10 may includeone radiating element or a vertical column of radiating elements. For anantenna having eight radiating units 10, the calibration device 20 mayinclude eight signal input ports 11. Each signal input port 11 isconnected to a corresponding RF transceiver (not shown) via abeamforming network. In a transmission mode, each RF transceiver of theantenna may output a subcomponent of the RF signal to be transmitted.The subcomponent of the RF signal arrives at a corresponding input port11 via the beamforming network to be input to the calibration device 20.At the calibration device 20, each subcomponent of the RF signal istransferred to a corresponding output port 12 through a correspondingtransmission line 13 that pass the subcomponents to the correspondingradiating units 10.

In order to collect a portion of the signals passing through thetransmission lines 13 from the signal input ports 11 to the radiatingunits 10, the calibration device 20 may include eight directionalcouplers 22. Each directional coupler 22 is a four-port device. Thecalibration device 20 further includes cascaded power combiners 24 thatcombine the outputs of the eight directional couplers 22 and connectthose outputs to a single calibration port 25. The directional couplers22, together with the cascaded power combiners 24, form a calibrationnetwork between the radiating units 10 and the calibration port 25. In acalibration operation for, e.g., a transmission path, a calibration testsignal may be transmitted by the RF transceivers. The calibration testsignal is transferred through the beamforming network and input to thecalibration device 20 at corresponding input ports 11. A small part ofthe power of each subcomponent of the calibration test signal is outputby a corresponding directional coupler 22 through its coupling port 23,and is then transferred to the cascaded power combiners 24. For anantenna having eight radiating units 10, the cascaded power combiners 24may be a 3-stage cascade Wilkinson power divider circuit that isconfigured to combine the coupling signals output by the coupling ports23 in pairs and ultimately combine the signals as a compositecalibration test signal. The composite calibration test signal is outputfrom the calibration device 20 via the calibration port 25. Thecalibration port 25 may be connected to a calibration transceiver. Thecalibration transceiver may compare the composite test signal with areference test signal so as to be capable of detecting the uniformity ofamplitude/phase of various transmission paths. Based on the comparison,the amplitude and/or phase characteristics of the signal components onthe transmission paths can be adjusted to compensate for the differencein amplitude/phase between the transmission paths so as to achieve adesired radiation pattern.

When there is a large number of radiating units, the prior artcalibration device includes a large number of couplers and powercombiners. Thus the size of the calibration device may be very large,making the calibration device hard to satisfy the requirement of highlyintegration and miniaturization of the antennas.

Moreover, the calibration network, which is composed of couplers andpower combiners, may itself introduce non-uniformities inamplitude/phase between paths. When a non-uniformity is observed at thecalibration port, it may not be possible to determine whether thenon-uniformity is caused by the beamforming and feeding network betweenthe RF transceiver and the radiating units or by the calibration networkbetween the radiating units and the calibration port.

When radiating units in an antenna array are used for services indifferent frequency bands (i.e., two or more frequency bands), thebeamforming networks for different frequency bands need to be calibratedseparately. Thus it is necessary to scale up a single calibration portinto a plurality of calibration ports to calibrate the beamformingnetworks for the different frequency bands separately.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a coupling device, anantenna calibration device, and an antenna device that overcomes atleast one of the deficiencies in the prior art.

According to a first aspect of the present disclosure, a coupling deviceis provided. This coupling device includes a plurality of couplers. Eachcoupler includes a transmission main line and a coupling subline. Thetransmission main line is used for providing an input end and an outputend. The coupling subline is coupled with the transmission main line toprovide two coupling ends. The coupling subline includes first andsecond parts located on opposite sides of the transmission main line anda third part connected between the first and second parts. The couplingsublines of the plurality of couplers are connected in series to providea first coupling output port and a second coupling output port. Thefirst part of the coupling subline of at least one coupler has a sharedsection with the third part of the coupling subline of an adjacentcoupler.

According to a second aspect of the present disclosure, an antennacalibration device is provided. The antenna calibration device includesa first power allocating part and a coupling device. This couplingdevice includes a plurality of couplers. Each coupler includes atransmission main line and a coupling subline. The transmission mainline is used for providing an input end and an output end. The couplingsubline is coupled with the transmission main line to provide twocoupling ends. The coupling subline includes first and second partslocated on opposite sides of the transmission main line and a third partconnected between the first and second parts. The coupling sublines ofthe plurality of couplers are connected in series to provide a firstcoupling output port and a second coupling output port. The first partof the coupling subline of at least one coupler has a shared sectionwith the third part of the coupling subline of an adjacent coupler. Thecoupling device is connected to a first power allocating part via thefirst coupling output port. The first power allocating part provides aplurality of first calibration ports.

According to a third aspect of the present disclosure, an antennacalibration device is provided. The antenna calibration device includesa plurality of directional couplers and a coupling device. The couplingdevice includes a plurality of couplers. Each coupler includes atransmission main line and a coupling subline. The transmission mainline is used for providing an input end and an output end. The couplingsubline is coupled with the transmission main line to provide twocoupling ends. The coupling subline includes first and second partslocated on opposite sides of the transmission main line and a third partconnected between the first and second parts. The coupling sublines ofthe plurality of couplers are connected in series to provide a firstcoupling output port and a second coupling output port. The first partof the coupling subline of at least one coupler has a shared sectionwith the third part of the coupling subline of an adjacent coupler. Aninput end of at least one coupler is connected to a coupling end of acorresponding directional coupler of a plurality of directionalcouplers.

According to a fourth aspect of the present disclosure, an antennadevice is provided. The antenna device includes a plurality of antennaradiating elements, a plurality of RF ports and a coupling devicecoupled between the plurality of antenna radiating elements and theplurality of RF ports. The coupling device includes a plurality ofcouplers. Each coupler includes a transmission main line and a couplingsubline. The transmission main line is used for providing an input endand an output end. The coupling subline is coupled with the transmissionmain line to provide two coupling ends. The coupling subline includesfirst and second parts located on opposite sides of the transmissionmain line and a third part connected between the first and second parts.The coupling sublines of the plurality of couplers are connected inseries to provide a first coupling output port and a second couplingoutput port. The first part of the coupling subline of at least onecoupler has a shared section with the third part of the coupling sublineof an adjacent coupler. Input ends of the couplers of the couplingdevice are connected to the corresponding ones of a plurality of RFports, and output ends of the couplers are connected to thecorresponding ones of the plurality of antenna radiating elements.

According to a fifth aspect of the present disclosure, an antenna deviceis provided. This antenna device includes a plurality of antennaradiating elements, a plurality of RF ports, and a plurality ofdirectional couplers and a coupling device which are coupled between aplurality of radiating units and the plurality of RF ports. Theplurality of radiating units, the plurality of RF ports and theplurality of directional couplers correspond to each other on aone-to-one basis. This coupling device includes a plurality of couplers.Each coupler includes a transmission main line and a coupling subline.The transmission main line is used for providing an input end and anoutput end. The coupling subline is coupled with the transmission mainline to provide two coupling ends. The coupling subline includes firstand second parts located on opposite sides of the transmission main lineand a third part connected between the first and second parts. Thecoupling sublines of the plurality of couplers are connected in seriesto provide a first coupling output port and a second coupling outputport. The first part of the coupling subline of at least one coupler hasa shared section with the third part of the coupling subline of anadjacent coupler. The input end of each of the plurality of directionalcouplers is connected to a corresponding RF port of the plurality of RFports, and the output end of each directional coupler is connected to acorresponding radiating unit of the plurality of radiating units, andthe coupling end of each directional coupler is connected to the inputend of a corresponding coupler of the coupling device.

According to a sixth aspect of the present disclosure, a couplingcircuit is provided. The coupling circuit includes a first couplingdevice. The coupling device includes a transmission line and twocoupling lines. The transmission line has a first end to receivesignals. The two coupling lines are located on opposite sides of thetransmission line and are coupled to the transmission line. An end ofeach coupling line close to the first end of the transmission lineprovides a coupled component of the signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating the basic structure andprinciple of a prior art calibration device;

FIG. 2 is a schematic structural diagram of an antenna that includes acoupling device according to an embodiment of the present invention;

FIG. 3 is a schematic structural diagram of a coupling device accordingto an embodiment of the present invention;

FIG. 4 is an enlarged view of a coupler included in the coupling deviceof FIG. 3;

FIG. 5 is a schematic structural diagram of a calibration deviceaccording to another embodiment of the present invention; and

FIG. 6 is a schematic structural diagram of a calibration device whichuses dual-directional couplers for scaling up the calibration ports.

DETAILED DESCRIPTION

The present invention will be described as follows with reference to theaccompanying drawings, in which certain embodiments of the presentinvention are shown. However, it is to be understood that the presentinvention may be embodied in many different forms and should not beconstrued as limited to the embodiments that are pictured and describedherein. Rather, these embodiments are provided so that this disclosurewill be thorough and complete, and will fully convey the scope of theinvention to those skilled in the art. It will also be appreciated thatthe embodiments disclosed herein can be combined in any way to providemany additional embodiments.

Like numbers refer to like elements throughout. In the figures, thethickness of certain lines, layers, components, elements or features maybe exaggerated for clarity. Well-known functions or constructions maynot be described in details for brevity.

As used herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” specify the presence of stated features, integers,steps, operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof. As used herein,the term “and/or” includes any and all combinations of one or more ofthe associated listed items.

It will be understood that when an element is referred to as being “on”,“attached” to, “connected” to, “coupled” with, “contacting”, etc.,another element, it can be directly on, attached to, connected to,coupled with or contacting the other element or intervening elements mayalso be present. In contrast, when an element is referred to as being,for example, “directly on”, “directly attached” to, “directly connected”to, “directly coupled” with or “directly contacting” another element,there are no intervening elements present. It will also be appreciatedby those of skill in the art that references to a structure or featurethat is disposed “adjacent” another feature may have portions thatoverlap or underlie the adjacent feature.

Spatially relative terms, such as “under”, “below”, “lower”, “over”,“upper”, “lateral”, “left”, “right” and the like, may be used herein forease of description to describe one element or feature's relationship toanother element(s) or feature(s) as illustrated in the figures. It willbe understood that the spatially relative terms are intended toencompass different orientations of the device in use or operation inaddition to the orientation depicted in the figures. For example, if thedevice in the figures is inverted, elements described as “under” or“beneath” other elements or features would then be oriented “over” theother elements or features. The device may be otherwise oriented(rotated 90 degrees or at other orientations) and the descriptors ofrelative spatial relationships used herein interpreted accordingly.

Embodiments of the present invention provide coupling devices forcalibrating an antenna. The coupling device can provide two independentcoupling output ports via appropriate connections between a plurality ofcouplers. The calibration devices according to embodiments of thepresent invention do not include a plurality of individual directionalcouplers and cascaded power combiners as in the prior art device of FIG.1, which reduces the size and cost of the calibration device. Moreover,the two independent coupling output ports can be used for eliminatingthe path difference caused by the calibration device itself, and thuscan detect non-uniformities in amplitude/phase along thetransmission/reception paths more accurately.

Referring now to FIG. 2, a schematic structural diagram of an antenna200 that includes a coupling device according to an embodiment of thepresent invention is shown. As illustrated in FIG. 2, the antenna 200includes an antenna array 210 and a calibration device 220.

The antenna 210 includes a plurality of (e.g., n) radiating units. Eachradiating unit 210-1, 210-2, . . . 210-n may include a single radiatingelement or a plurality of radiating elements (e.g., a column ofradiating elements). Each radiating element completes radiation of atransmit signal and performs front-end reception of a receive signal. Inthe following text, radiating units 210-1, 210-2, . . . 210-n may alsobe collectively referred to as “radiating unit 210”.

The calibration device 220 includes a plurality of signal input ports211, a plurality of signal output ports 212 that correspond to thesignal input ports 211 on a one-to-one basis, and a coupling device 230that is connected between the signal input ports 211 and the signaloutput ports 212. The coupling device 230 includes a first couplingoutput port 225 a and a second coupling output port 225 b which canprovide independent outputs.

The coupling device 230 may operate bi-directionally. At the time oftransmission, RF signals (e.g., from a beamforming network or otherfeeding network) enter the coupling device 230 via the individual signalinput ports 211, and are then passed to the corresponding radiatingunits 210 via the corresponding signal output ports 212. The couplingdevice 230 collects a portion of the energy of the RF signalstransmitted between each signal input port 211 and its correspondingsignal output port 212. The collected signal energy can be output fromthe calibration device 220 via the first coupling output port 225 a andthe second coupling output port 225 b. Preferably, the collected energyis a small part of the energy of the input signals. During normalreception, RF signals from the radiating units 210 may enter thecoupling device 230 through the signal output ports 212 and be outputfrom the signal input ports 211; during reception calibration, thecalibration test signal may enter the coupling device 230 via the firstcoupling output port 225 a or the second coupling output port 225 b andbe output from the signal input ports 211. Ideally, there is certainisolation between the signal output ports 212 and the coupling outputports 225 a and 225 b.

As is further shown in FIG. 2, the antenna 200 may further include abeamforming network 240, RF transceiver(s) 250 and an antenna interfaceunit 260.

The antenna interface unit 260 includes processors for receiving adigital signal from a baseband unit (not shown) and providing adigitized received signal to the baseband unit. The baseband unit may bea part of a main control system of a base station (not shown). The RFtransceivers 250 may perform various signal processing, such as, but notlimited to, digital processing, digital-to-analog or analog-to-digitalconversion, baseband/intermediate frequency (IF)/RF conversion, lownoise amplification and filtering. Beamforming network 240 may comprisephase-shifters or feeding power allocating circuits for applyingpredetermined gain/phase adjustment to signals of different paths fromthe RF transceivers and feeding the signals to respective radiatingunits 210, or for receiving signals from respective radiating units 210and transferring the signals to respective RF transceivers 250.

When the antenna 200 operates in a transmission mode, antenna interfaceunit 260 receives a signal to be transmitted from the baseband unit,divides the signal into n identical subcomponents (for example, thenumber of subcomponents may equal to the number of radiating units 210),applies gain and phase adjustments to each subcomponent, and providesthe subcomponents to corresponding RF transceivers 250. Thesubcomponents are converted into analog RF signals by the RFtransceivers 250, and arrive at corresponding radiating units 210 viathe beamforming network 240. The RF signals are radiated by theradiating units 210 and the radiated RF signals are interfered andsuperimposed together to form a desired radiation pattern.

When the antenna 200 operates in a reception mode, each radiating unit210 receives different subcomponents of the received RF signal. Eachsubcomponent of the received RF signal is provided to a corresponding RFtransceiver 250, converted into a digital subcomponent at the RFtransceiver 250 and delivered to antenna interface unit 260. Antennainterface unit 260 applies gain and phase adjustments to the receiveddigital subcomponents, and combines the digital subcomponents to form acomposite received signal.

Antenna 200 may perform complicated beamforming manipulation bycontrolling the gains and phase shifts. For example, the antenna 200 mayelectronically adjust the beam width, beam shape and pointing directionof the antenna beam by changing the gains (via the power allocatingcircuits) and the phase shifts (via the phase shifters) in thebeamforming network 240.

However, the transmission paths through the antenna 200 may havedifferent propagation characteristics, such that even if the desiredgains and phase shifts are applied to the signals traversing each path,the resulting antenna beam may differ from the expected (desired)antenna beam. Moreover, during operation of the smart antenna, relativechanges may occur between the different paths. Therefore, it may benecessary to detect, calibrate and compensate for the differences andchanges in the transmission characteristics between the paths.

By collecting a portion of the signals on the transmission and receptionpaths, the calibration device 220 (mainly including a coupling device230) may be used to calibrate the paths to compensate fornon-uniformities in amplitude/phase between individual transmission andreception paths. In some embodiments, the antenna 200 may also include acalibration transceiver 270. The coupling output ports 225 a and 225 bof the calibration device 220 are coupled to the calibration transceiver270 via, for example, a RF cable. The calibration device 220 and thecalibration transceiver 270 may be used for monitoring the values of thegains and the phases of all the transmission and reception paths so asto be capable of adjusting them. The calibration device 220 may performinitial calibration and continuous monitoring and adjustment duringnormal use of the antenna 200.

To calibrate the transmission channels, a calibration test signal istransmitted from the antenna interface unit 260 to the radiating units210. A portion of the energy of the calibration test signal is extractedthrough the coupling device 230 and is output through the couplingoutput ports 225 a and 225 b to the calibration transceiver 270. Thecalibration transceiver 270 performs an operation similar to theoperation of the RF transceiver(s) 250 and measures a compositecalibration test signal. The calibration transceiver 270 and/or theantenna interface unit 260 implement an algorithm to determine thenecessary adjustments of the gain and the phase of the signals on thetransmission paths. Antenna interface unit 260 then carries out theadjustment.

Various algorithms for calibration are already known to a person skilledin the art, and thus will not be further described herein.

In order to calibrate the reception paths, the calibration transceiver270 transmits the test signal to the coupling output ports 225 a and 225b. A portion of the energy of each subcomponent of the calibration testsignal is transmitted, via the coupling device 230, to the respectivereception paths where the subcomponents are processed by the respectiveRF transceivers 250 and provided to antenna interface unit 260. Antennainterface unit 260 receives different versions of the calibration testsignals from the reception paths and uses a suitable algorithm to changethe gain and phase of the signals received from the reception paths inorder to form an appropriate antenna beam.

FIG. 3 is a schematic structural diagram of a coupling device 300according to an embodiment of the present invention. The coupling device300 in FIG. 3 may be used, for example, to implement the coupling device230 of FIG. 2. The coupling device 300 includes a plurality of couplers.For a smart antenna having eight radiating units 210, the couplingdevice 300 may include eight couplers 302-1, 302-2 . . . 302-8 thatcorrespond to the eight radiating units 210 on a one-to-one basis. Forsimplicity, couplers 302-1, 302-2 . . . 302-8 hereinafter may beindividually and/or collectively referred to as “coupler(s) 302”. Inother embodiments, the number of couplers may be more or less than eightcouplers 302. FIG. 4 is an enlarged view of one of the couplers 302 thatis included in the coupling device 300 of FIG. 3.

As illustrated in FIG. 4, coupler 302 includes a main transmission line303 and a coupling subline 305. The main transmission line 303 may beused for transmitting signals between a beamforming network (e.g.,beamforming network 240 of FIG. 2) and a corresponding radiating unit210. The input end 304 a of the main transmission line 303, whichcorresponds to signal input port 211 in FIG. 2, may be connected to thebeamforming network 240. The output end 304 b of the main transmissionline 303, which corresponds to signal output port 212 in FIG. 2, may beconnected to a radiating unit 210 that corresponds to the particularcoupler 302.

The coupling subline 305 includes first and second coupling portions 307a and 307 b which each are configured to couple with the maintransmission line 303. The first and second coupling portions 307 a and307 b may be located on opposite sides of the main transmission line303. The first and second coupling portions 307 a and 307 b and the maintransmission line 303 may be implemented, for example, using coaxiallines, rectangular waveguides, circular waveguides, strip lines,microstrip transmission lines and/or any other transmission lines.Coupling between the first and second coupling portions 307 a, 307 b andthe main transmission line 303 may be achieved by various known couplingtechnologies, including but not limited to aperture coupling, parallelcoupling, branch coupling and matching double-T. In some embodiments,the coupling subline 305 and the main transmission line 303 may beimplemented as edge-coupled microstrip transmission lines, so that thestructure of the calibration device is more compact and meets therequirements for miniaturization. In the three-line coupling structureformed by the first and second coupling portions 307 a and 307 b and themain transmission line 303 that is shown in FIG. 4, 304 a is an inputend, 304 b is an output end, 306 a and 306 b are coupling ends, and 308a and 308 b are isolation ends. A third connection portion 307 c of thecoupling subline 305 connects the first and second coupling portions 307a and 307 b. The shape of the third connection portion 307 c is notlimited. The electrical length of the connection portion 307 c may bedesigned so that its impedance matches the impedance of the three-linecoupling structure. As a result, when a signal is input at the input end304 a, the coupled components of the signal are only transmitted throughthe coupling ends 306 a and 306 b, and no power is output on the thirdconnection portion 307 c between the isolation ends 308 a and 308 b.

Returning to FIG. 3, the same reference signs in FIG. 3 and FIG. 4represent the same components. Firstly, coupling sublines 305 ofcouplers 302-1 to 302-8 are connected in series and the seriesconnection may be terminated on either end by a first coupling outputport 325 a and a second coupling output port 325 b (corresponding to 225a and 225 b in FIG. 2). By connecting the coupling sublines 305 of aplurality of couplers 302 in series, the coupling device 300 may havethe following ability: when a signal is injected at the input end 304 aof any individual coupler 302-1 to 302-8, two coupled components of theinjected signal can always be obtained from the two coupling output port325 a and 325 b. The two coupled components are obtained by coupling andtransferring the injected signal through two different paths that areindependent of each other. For example, when a signal is injected at theinput end 304 a of coupler 302-5, coupled components are obtained atcoupling ends 306 a and 306 b of the coupler 302-5, respectively.Thereafter, according to the coupling theory, the coupled component atthe coupling end 306 a sequentially passes through the coupling sublinesof couplers 302-4, 302-3, 302-2 and 302-1 to arrive at the couplingoutput port 325 a; the coupled component at the coupling end 306 bsequentially passes through the coupling sublines of couplers 302-6,302-7 and 302-8 to arrive at the coupling output port 325 b.

For an individual coupler 302, a first path from the input end 304 a tothe first coupling output port 325 a and a second path from the inputend 304 a to the second coupling output port 325 b will impart differentamplitude/phase changes to the signals transferred thereon. However, forall the couplers 302, a sum of the amplitude/phase changes of the firstpath and the amplitude/phase changes of the second path is fixed. Forexample, in FIG. 3, the sum approximately equals an amount of change inamplitude/phase caused by the electrical length of the overlappedcoupling sublines of the eight couplers. In this way, for the individualtransmission paths connected to the corresponding couplers, theamplitude/phase uniformity between these transmission paths can bedetermined by comparing the difference between the sum values of thecoupling output ports 325 a and 325 b. For the individual couplers 302in the coupling device 300, it is not necessary to ensure that they haveidentical circuit structures, since the difference in circuit structurescan be eliminated in the calibration algorithm based on the two coupledcomponents at the coupling output ports 325 a and 325 b. According tothe characteristics of signal propagation in the circuit structure, aperson skilled in the art knows how to modify the calibration algorithmin the prior art. For example, it is possible to modify the directcomparison of the difference between the output signals from thecalibration ports of the individual transmission paths in the prior artas comparison between the sum values of signals from the coupling outputports 325 a and 325 b of the individual transmission paths. Otherdetails of the calibration algorithm will not be described here.

Secondly, a coupling subline 305 of at least one coupler 302 has ashared section with a coupling subline 305 of an adjacent coupler 302.Specifically, one of the two coupling portions 307 a, 307 b of thecoupling subline 305 of at least one coupler 302 has a shared sectionwith a connection portion 307 c of the coupling subline 305 of anadjacent coupler 302. For example, as shown in FIG. 3, coupling portion307 b of the coupling subline 305 of coupler 302-1 serves as at leastone part of the connection portion 317 c of adjacent coupler 302-2.Since the coupling sublines 305 of adjacent couplers 302 aresequentially connected in series, that is, in an order of 307 c, 307 b,317 a, 317 c, when 307 b and 317 c have a shared section, 307 c and 317a also has a shared section. For example, in FIG. 3, coupling portion317 a serves as a section 307 c-1 of connection portion 307 c.Accordingly, an isolation end 308 a of coupler 302-1 is connected to acoupling end 316 a of coupler 302-2, and the other isolation end 308 bof coupler 302-1 is connected to the isolation end 318 a of coupler302-2, and a coupling end 306 b of coupler 302-1 is connected to anisolation end 318 b of coupler 302-2 via the connection portion 317 c.In this way, adjacent couplers 302-1 and 302-2 present an interleavedarrangement. That is, the input end 304 a of coupler 302-1 and the inputend 314 a of coupler 302-2 are remote from each other, while the outputends 304 b and 314 b are close to each other.

When a signal is injected at an input end 304 a of coupler 302-1,coupled components are output from coupler 302-1 at the coupling ends306 a and 306 b. The coupled component at coupling end 306 a may pass tothe first coupling output port 325 a. The coupled component at couplingend 306 b passes to the coupling end 316 b of coupler 302-2 along thecoupling subline 305 of coupler 302-2, and continues to pass along theserially connected coupling sublines 305 of couplers 302-3 to 302-8 inthe same manner so that the coupled component at coupling end 306 b of202-1 is ultimately output through the second coupling output port 325b.

Due to the shared section between the coupling sublines 305 of at leastone coupler 302 and its adjacent coupler 302, as compared to usingindividual couplers, a path from the input end of one coupler to thecoupling output port is reduced, which decreases the insertion loss ofthe coupling output port relative to the input end. This arrangement ofcouplers is also more compact, further reducing the size of the couplingdevice 300. A simulation for a specific embodiment of the couplingdevice 300 indicates that, as compared to using individual couplers, thesize of the coupling device 300 is reduced by 44%, and the insertionloss of the coupling ports is reduced by 1.6 dB. In addition, thecoupling device 300 can also have improved return loss and couplingflatness.

It should be appreciated that, although FIG. 3 shows that each coupler302 shares a section of the coupling subline 305 with an adjacentcoupler 302, in other embodiments, it is also possible that only onecoupler 302 shares a section of the coupling subline 305 with anadjacent coupler 302 while the other couplers 302 still only have theircoupling sublines 305 connected in series. Such embodiments also fallwithin the scope of the present invention.

Returning to FIG. 2, in some embodiments, a first power allocating part231 is connected to the first coupling output port 225 a. The firstpower allocating part 231 has a plurality of first calibration ports(e.g., calibration ports 232-1 and 232-2 shown in FIG. 2). The firstpower allocating part 231 may equally divide and/or unequally divide thepower of the signals output at the first coupling output port 225 a. Thenumber of first calibration ports included in the first power allocatingpart 231 is not limited to two as shown in FIG. 2. The first powerallocating part 231 may be implemented, for example, using any of thefollowing techniques: a 1 to N Wilkinson-type or other type of powersplitter, a select-1-from-N switch array, or a circuit or device havingsimilar functionality. In order to reduce the return loss of the firstcalibration ports relative to the signal input ports 211 of couplingdevice 230, the first power allocating part 231 may also include a powerattenuator.

In a further embodiment, the first power allocating part 231 may includea frequency demultiplexing element. The frequency demultiplexing elementsplits signals output through the first coupling output port 225 a basedon frequency such that at least two of the plurality of firstcalibration ports 232 may output signals in different frequency bands.For example, the first calibration ports 232-1 and 232-2 in FIG. 2 maycorrespond to different frequency bands, respectively. The frequencydemultiplexing element may include filters of various knowntechnologies. In a specific example, a signal from the first couplingoutput port 225 a may be subdivided into two parts by a power divider inthe first power allocating part at first. At least one of the outputbranches may be provided with band pass (or other suitable) filters fordifferent frequency bands. Dividing the signals output by the couplingdevice by frequency is beneficial when the radiating units in theantenna array are used to support service in multiple frequency bandsbecause it can prevent mutual interference between signals in differentfrequency bands that are output by the coupling device which might occurduring subsequent signal processing. To ensure the uniformity ofcalibration channels for signals in different frequency bands in thecalibration device 220, it is preferable to provide uniformamplitude/phase characteristics to signals transferred on paths from thefirst coupling output port 225 to respective first calibration portsused for different frequency bands. For example, in FIG. 2, whencalibration ports 232-1 and 232-2 are used for different frequencybands, a first path from 225 a to 232-1 and a second path from 225 a to232-2 may have mirror-symmetrical circuit arrangements.

A second power allocating part 233 may be coupled to the second couplingoutput port 225 b to be scaled up into a plurality of second calibrationports (e.g., calibration ports 234-1 and 234-2 illustrated in FIG. 2).In some embodiments, the second power allocating part 233 may have acircuit arrangement which is mirror-symmetrical with the first powerallocating part 231. When the first power allocating part 231 includes afrequency demultiplexing element, the second power allocating part 233may also include the same frequency demultiplexing element, such thatthe plurality of second calibration ports correspond to the respectiveplurality of first calibration ports. A first calibration port may beused in a pair with a corresponding second calibration port (e.g., 232-1and 234-1 are used in a pair) for calibrating reception/transmissionpaths for a particular frequency band. In other embodiments, the secondpower allocating part 233 may be different from the first powerallocating part 231. A first calibration port (such as 232-1) and asecond calibration port (such as 234-1) can be used as a pair forcalibrating the corresponding reception/transmission paths as long asthey are used for the same frequency band.

In some embodiments, the calibration device may also include a pluralityof directional couplers in addition to the coupling device. Eachdirectional coupler may include a transmission line and a coupling linethat are coupled to each other. The transmission lines may be feed linesfor transferring signals between corresponding RF ports of a beamformingnetwork and corresponding radiating elements. A coupling line is used toextract a portion of the signal energy transferred on the feed line andtransfer it to the coupling device according to the embodiments of thepresent invention as described with reference to FIGS. 2-4.

FIG. 5 is a schematic structural diagram of a calibration device 520according to a further embodiment of the present invention. Similar toFIG. 2, the calibration device 520 is connected to an antenna array 510that includes a plurality of radiating units. The specific structure ofthe antenna array 510 is similar to the antenna array in FIG. 2, andwill not be described in detail herein. The calibration device 520includes a coupling device 530 and a plurality of directional couplers522. Each directional coupler 522 may be a four-port device, whichincludes a transmission line 513 and a coupling line that is coupled tothe transmission line 513. The two ends of the transmission line 513 arean input end and an output end, respectively. The end of the couplingline that is close to the input end is a coupling end 523, while theopposite end is an isolation end 526. Each directional coupler 522 maybe connected to a beamforming network via a signal input port 511 as aninput end and with a corresponding radiating unit 510 via a signaloutput end 512 as an output end. Each transmission line 513 extendsbetween a respective one of the signal input ports 511 and acorresponding signal output port 512, and is a part of a transmissionpath extending between a RF transceiver and the corresponding radiatingunit. The transmission line 513 may be implemented as, for example, amicrostrip RF transmission line. Each coupling end 523 is connected toan input port of the coupling device 530 (e.g., connected to an inputend 304 a of each coupler 302 shown in FIG. 3) for transferring a smallpart of the energy of the calibration test signal transmitted througheach transmission path. The isolation end 526 is connected to a matchedload, which may be, for example, a 50 Ohm resistor.

Similar to the coupling output ports 225 a and 226 b in FIG. 2, thecoupling device 530 has a first coupling output port 525 a and a secondcoupling output port 525 b. The coupling device 530 may adopt thestructure as discussed above with reference to FIGS. 3-4. Each outputport 531 of the coupling device (e.g., an output end 304 b of eachcoupler 302 shown in FIG. 3) is connected to a matched load, which mayalso be, for example, a 50 Ohm resistor.

When there is a reflection signal from a radiating unit 510, since thereis a certain degree of isolation between an output port 512 and acoupling end 523 of a directional coupler 522, it is possible toeffectively suppress the reflection signal from entering the couplingdevice 530 and from being output from the coupling output ports 525 aand 525 b. Therefore, as compared with the coupling device 230 of thecalibration device 220 in FIG. 2 which is directly connected between thebeamforming network and the radiating units, the calibration device 520in FIG. 5 can use directional couplers to absorb reflection signals fromthe radiating units. In addition, since the directional couplers can belocated proximate the radiating units, the calibration device 520 cancalibrate the entire feed network at the input ports of the radiatingunits, thereby making the calibration more accurate and effective. In aspecific example of a simulated calculation, as compared with thecalibration device 220, the coupling accuracy of the coupling device 520is increased from ±4.85 dB to ±2 dB, and the phase accuracy is increasedfrom ±21° to ±3°.

According to another aspect of the present invention, as a substitutedfor the Wilkinson power divider, the first power allocating part 231and/or the second power allocating part 233 of FIG. 2 may use adual-directional coupler to scale up the coupling output port 225 a or225 b of the coupling device 230 into a plurality of calibration ports.When radiating units in the smart antenna are used to support servicesin two or more frequency bands, the plurality of calibration ports,which are obtained by scaling up, can be used for calibration of thedifferent frequency bands.

FIG. 6 is a schematic structural diagram of a calibration device 620which employs dual-directional couplers to scale up a calibration port.The calibration device 620 includes a coupling device 630 similar to thecoupler device 230 in FIG. 2, which includes a plurality of input ports611, a plurality of output ports 612 and coupling output ports 625 a and625 b. The coupling device 630 may adopt the structure as discussedabove with reference to FIGS. 3-4. The calibration device 620 alsoincludes a power distribution portion 631 for scaling up the couplingoutput port 625 a into a plurality of calibration ports 632-1 and 632-2.The power distribution portion 631 includes a dual-directional coupler635. The dual-directional coupler 635 includes a transmission line thatis connected to the coupling output port 625 a and two coupling linesthat are coupled to the transmission line on opposite sides thereof,thereby having six ports. The through port 637 of the transmission linemay be grounded via a matched load end so as to reduce reflectionsignals that enter the coupling device 630. The matched load may be, forexample, a 50 Ohm resistor. In some embodiments, isolation ports 636 aand 636 b that are adjacent port 637 on two coupling lines may begrounded via a matched load end to avoid interference of the reflectionsignals. In some embodiments, as illustrated in FIG. 6, isolation ports636 a and 636 b may be connected to respective T-shaped bias circuits.The bias signal ports 638-1 and 638-2 of the T-shaped bias circuits areused for applying respective DC bias signals. The ports 639 a and 639 bmay be terminated with fan-shaped traces via matched loads (e.g., 50 Ohmresistors) to allow DC signals to pass and to make high frequencysignals virtually grounded. Accordingly, when a RF signal is input fromthe port 625 a and a DC bias signal is applied at the bias signal port638-1, a composite signal of a coupled component of the RF signal andthe DC bias signal will be obtained from the coupling port 632-1.Likewise, a composite signal of a coupled component of the RF signal andthe DC bias signal applied via the bias signal port 638-2 will beobtained from the coupling port 638-1.

When a Wilkinson power divider is used, there is a direct connectionbetween the calibration ports 632-1 and 632-2, and DC bias signals addedto different calibration ports may cause mutual interference. Therefore,a DC block is usually needed between two calibration ports in practice.In contrast, the use of a dual-directional coupler 635 can prevent DCconnections between different calibration ports and achieve betterperformance than a DC block at a lower cost. In addition, thedual-directional coupler 635 achieves better return loss than theWilkinson power divider and reduces the size of the calibration device.

It will be appreciated that although FIG. 5 shows that the powerdistribution circuit 631 is coupled to a coupling device providing twoindependent coupling output ports according to an embodiment of thepresent invention, in other embodiments, the power distribution circuit631 may be connected with calibration ports of various calibrationdevices in the prior art for scaling up the number of calibration ports.

The foregoing is illustrative of the present disclosure and is not to beconstrued as limiting thereof. Although exemplary embodiments of thisinvention have been described, those skilled in the art should readilyappreciate that many variations and modifications are possible in theexemplary embodiments without materially departing from the novelteachings and advantages of this invention. Accordingly, all suchvariations and modifications are intended to be included within thescope of this invention as defined in the claims. The invention isdefined by the following claims, with equivalents of the claims to beincluded therein.

That which is claimed is:
 1. A coupling device, comprising: a pluralityof couplers, each coupler including: a main transmission line having aninput end and an output end; and a coupling subline that is coupled tothe main transmission line, the coupling subline including a first partand a second part that are located on opposite sides of the maintransmission line and a third part that connects the first and secondparts; wherein the coupling sublines of the plurality of couplers areconnected in series to provide a first coupling output port and a secondcoupling output port, wherein the first part of the coupling subline ofa first coupler of the plurality of couplers has a first shared sectionwith the third part of the coupling subline of a second coupler of theplurality of couplers that is adjacent the first coupler.
 2. Thecoupling device according to claim 1, wherein the third part of thecoupling subline of the first coupler has a second shared section withthe first part of the coupling subline of the second coupler.
 3. Thecoupling device according to claim 1, wherein the first and second partsof the second coupler are coupled in parallel to the main transmissionline of the second coupler on opposite sides thereof, and the third partof the second coupler includes a segment that extends in parallel to thefirst and second parts, and the first shared section is at least onepart of the segment.
 4. The coupling device according to claim 1,wherein the length of the third part of the coupling subline of thesecond coupler of the plurality of couplers is configured tosubstantially block energy coupled from the main transmission line ofthe second coupler to the first and second part so that coupling sublineof the second coupler from passing to the third part of the couplingsubline of the second coupler.
 5. The coupling device according to claim1, wherein an input end of at least one coupler is connected to acoupling end of a corresponding directional coupler.
 6. The couplingdevice according to claim 5, wherein an output end of the at least onecoupler is connected to a matched load.
 7. The coupling device accordingto claim 5, wherein an output end of the corresponding directionalcoupler is connected to a matched load.
 8. An antenna calibrationdevice, comprising: a first power allocating part, and a coupling deviceaccording to claim 1, wherein the coupling device is connected to thefirst power allocating part via the first coupling output port, and thefirst power allocating part has a plurality of first calibration ports.9. The antenna calibration device according to claim 8, furthercomprising a second power allocating part, wherein the coupling deviceis connected to the second power allocating part via a second couplingoutput port, and the second power allocating part has a plurality ofsecond calibration ports.
 10. The antenna calibration device accordingto claim 8, wherein the first power allocating part includes a frequencydemultiplexing element, and at least two of the plurality of firstcalibration ports are frequency selective ports.
 11. The antennacalibration device according to claim 10, wherein paths between thefirst calibration ports and the first coupling output port have uniformamplitude and phase characteristics.
 12. An antenna calibration device,comprising: a plurality of directional couplers; and a coupling deviceaccording to claim 1, wherein an input end of at least one coupler ofthe coupling device is connected to a coupling end of a correspondingdirectional coupler of the plurality of directional couplers.
 13. Theantenna calibration device according to claim 12, wherein an output endof the at least one coupler is connected to a matched load.
 14. Theantenna calibration device according to claim 12, wherein an output endof the corresponding directional coupler is connected to a matched load.15. An antenna, comprising: a plurality of radiating units; a pluralityof radio frequency ports; the coupling device according to claim 1coupled between the plurality of radiating units and the plurality ofradio frequency ports, wherein the input ends of the couplers of thecoupling device are connected to corresponding ones of the plurality ofradio frequency ports, and the output ends of the couplers are connectedto corresponding ones of the plurality of radiating units.
 16. Anantenna, comprising: a plurality of radiating units; a plurality ofradio frequency ports; a plurality of directional couplers coupledbetween the plurality of radiating units and the plurality of radiofrequency ports, wherein the plurality of radiating units, the pluralityof radio frequency ports and the plurality of directional couplerscorrespond to one another on a one-to-one basis; and the coupling deviceis the coupling device according to claim 1, wherein an input end ofeach of the plurality of directional couplers is connected to acorresponding radio frequency port of the plurality of radio frequencyports, and an output end of the each directional coupler is connected toa corresponding radio unit of the plurality of radiating units, and acoupling end of the each directional coupler is connected to an inputend of a corresponding coupler of the coupling device.